As described in commonly assigned U.S. Pat. No. 5,320,643, incorporated herein by reference, a cardiac pacemaker is an electrical device implemented to rectify an abnormal heart's natural pacing function by delivering appropriately timed electrical stimulation signals designed to cause the myocardium of the heart to depolarize. Many traditional devices unnecessarily pace in the ventricle. Inappropriate ventricular pacing may have short-term hemodynamic effects and may not be desirable when allowed to continue for an extended period of time. Several devices designed to reduce unnecessary pacing in the ventricle have been developed. An example of such a device is described in commonly assigned U.S. Patent Application Publication No. 2003/0078627, the contents of which are hereby incorporated by reference.
Further, the amplitude and pulse width of the pacing pulses must be of such a magnitude above the stimulation threshold to maintain capture so as to prevent serious complications. Yet, it is desirable that these pacing output parameters are no higher than a reasonable safety margin above the stimulation threshold in order to prolong battery life. The patient's stimulation thresholds in the atrium and ventricle often fluctuate in the short term, and gradually change over the long term. Some devices have been developed to provide atrial capture management (ACM) in traditional dual chamber pacing devices. An example of such a device is described in commonly assigned U.S. Patent Application Publication No. 2004/0030358, incorporated herein by reference.